Multi-Stage Trochoidal Vacuum Pump

ABSTRACT

A vacuum pump includes first, second, third and fourth pump stages. Each pump stage has a trochoidal-shaped cavity and a rotor that rotates within the respective cavity. Each cavity has a volume determined by the depth of the cavity and a generally corresponding thickness of the rotor. The fourth stage has a largest volume and receives gas at an input pressure. The fourth stage outputs the gas to the third stage at a second pressure higher than the input pressure. The cavity of each successive stage (third, second and first) has a smaller volume and outputs the gas at a higher pressure than the previous stage. The last (first) stage outputs the gas to the atmosphere. The rotors in the stages rotate about a common pump shaft. Each rotor has a multiple vertices that follow the inner perimeter surface of the respective cavity without contact and without requiring additional seals.

RELATED APPLICATIONS

The present application claims the benefit of priority under 35 USC § 119(e) to U.S. Provisional Application No. 60/894,914, filed on Mar. 15, 2007.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is generally in the field of vacuum pumps for removing gases from a system.

2. Description of the Related Art

A mass spectrometer can be maintained at high vacuum by suitable pumps; however, the problem of sample introduction from an elevated pressure to a vacuum pressure usually requires substantial flow. This requirement causes the pumping problem to be difficult with respect to the power needed and the wide dynamic range of the pressures. Often, pumping over a wide dynamic range is accomplished with many pump stages. The pump stages may all operate on the same principle or different stages may operate on different principles. The stages may all be in a common housing or the stages may be in separate housings. Many pumps are commercially available to accomplish the pumping task. Such pumps are categorized as “roughing” pumps. Available pumps generally go from atmospheric pressure to pressures in the Torr or milli-Torr range. Usually, the commercially available pumps are very large and heavy and have a capacity that is more than is necessary for a miniature device. Although additional pumping capacity may be desirable so that a pumping system is not operated at its limits, the additional size and weight of a pump with such additional capacity may preclude the use of a pumping system in a miniature device, such as, for example, a portable mass spectrometer.

In a portable mass spectrometer, a vacuum pump that provides a mass flow rate of 1 to 5 SCCM (standard cubic centimeters per minute) is desirable, with a preference for a mass flow rate of 5 SCCM. The desired vacuum pump also reduces the pressure from atmospheric pressure down to approximately 1 Torr in order to produce a sufficient pressure drop in the final admittance stage to the high vacuum system that contains the gas analyzer component of the mass spectrometer. In addition to the foregoing requirements, in order to make the overall mass spectrometer portable, the weight of the vacuum pump is preferably less than approximately one pound and the power requirement for the vacuum pump is preferably less than approximately 10 watts.

Common commercially available vacuum pumps that provide the desired flow rates over the dynamic pressure range include piston pumps, diaphragm pumps, and scroll pumps; however, such pumps are not commercially available with the desired low weight and low power.

SUMMARY OF THE INVENTION

One aspect of embodiments in accordance with the present invention is a multi-stage vacuum pump which includes a plurality of pump stages operating on the principle of the eccentric trochoid. The pump includes at least a first stage and a second stage. The first stage includes a first housing having a first inner cavity bounded by a trochoid-curved interior wall that forms at least a first lobe and a second lobe of the first inner cavity. The first inner cavity has a first volume determined by a combined area of the first and second lobes of the first inner cavity and a depth of the first inner cavity. The first housing has at least a first inlet passage communicating with the first lobe of the first inner cavity and has at least a first outlet passage communicating with the second lobe of the first inner cavity. The first housing further includes at least a first interconnecting passage between the first lobe and the second lobe. A first rotor in the first housing has at least three sides and at least three vertices at the intersection of each pair of adjacent sides. The first rotor has a thickness selected to fit within the depth of the first inner cavity. The first rotor rotates about a first circular cam that is eccentrically mounted on a common shaft to cause the three vertices to follow the trochoid-curved interior wall of the first inner cavity and to alternately form suction chambers and compression chambers between the sides of the first rotor and the trochoid curved interior wall of the first inner cavity. The lengths of the sides of the first rotor are selected to be adjacent to but not touching the trochoid curved interior wall. As the first rotor rotates within the first inner cavity, a first side of the first rotor forms a first suction chamber proximate the first inlet passage to draw gas into the first lobe of the first inner cavity. As the first rotor continues to rotate, the first suction chamber becomes a first compression chamber proximate a first end of the first interconnecting passage that forces the gas through the first interconnecting passage and into a second suction chamber formed in the second lobe by a second side of the first rotor proximate a second end of the first interconnecting passage. As the first rotor continues to rotate, a third side of the first rotor forms a third suction chamber proximate the first inlet passage to draw gas into the third suction chamber. Subsequently, the second suction chamber becomes a second compression chamber that forces the gas out of the second lobe of the first inner cavity via the first outlet passage as gas continues to be drawn into the third suction chamber.

The second stage includes a second housing having a second inner cavity bounded by a trochoid-curved interior wall having at least a first lobe and a second lobe, and having a second inlet passage, a second outlet passage, and a second interconnecting passage. The inlet passage of the second housing is connected to the outlet passage of the first housing. The second inner cavity has a second volume less than the first volume. The second housing includes a second rotor similar to the first rotor but with at least one dimension smaller than a corresponding dimension of the first rotor to correspond to the smaller second volume of the second inner cavity. The second rotor rotates about a second circular cam eccentrically mounted on the common shaft to cause the three vertices of the second rotor to follow the trochoid-curved interior wall of the second inner cavity and to alternately form suction chambers and compression chambers between the sides of the second rotor and the trochoid-curved interior wall of the second cavity. The rotation of the second rotor forms suction chambers to draw gas into the first lobe of the second inner cavity via the second inlet passage and forms compression chambers to discharge gas out of the second lobe of the second inner cavity via the second outlet passage.

Another aspect of embodiments in accordance with the present invention is a vacuum pump having first, second, third and fourth pump stages. Each pump stage has a trochoidal-shaped cavity and a rotor that rotates within the respective cavity. Each cavity has a volume determined by the depth of the cavity and a generally corresponding thickness of the rotor. The fourth stage has a largest volume and receives gas at an input pressure. The fourth stage outputs the gas to the third stage at a second pressure higher than the input pressure. The cavity of each successive stage (third, second, first) has a smaller volume and outputs the gas at a higher pressure than the previous stage. The last (first) stage outputs the gas to the atmosphere. The rotors in the stages rotate about a common pump shaft. Each rotor has a multiple vertices that follow the inner perimeter surface of the respective cavity without contact and without requiring vertex seals.

Another aspect of embodiments in accordance with the present invention is a pump that comprises a first stage having a first trochoidal-shaped cavity having a first volume and a second stage having a second trochoidal-shaped cavity having a second volume greater than the first volume. The first stage has a first input port and a first output port, and the second stage has a second input port and a second output port. A first rotor rotates eccentrically within the first cavity about a first cam, and a second rotor rotates eccentrically within the second cavity about a second cam. A common shaft rotates the first cam and the second cam to cause the first and second rotors to rotate about a common axis. A first interconnection conduit that couples the second output port to the first input port so that gas compressed in the second stage is further compressed in the first stage. Preferably, the first cavity has substantially the same shape and area as the second cavity, and the second cavity has a greater depth than the first cavity. Also preferably, the first rotor and the second rotor have substantially the same area, and the second rotor has a greater thickness than the first rotor. Preferably, the rotors do not include any seals. In particular, each vertex of each rotor has a continuous, uninterrupted contour.

Preferably, each of the first output port and the second output port has a respective output check valve that opens to allow gas to exit the respective cavity via the respective output port when the pressure on the side of the check valve proximate the cavity is sufficiently greater than the pressure on the opposite side of the check valve. Each output check valve closes to prevent gas from entering the respective cavity via the respective output port when the pressure on the side of the check valve proximate the cavity is insufficient to force the check valve open. The second input port also has a check valve that opens to allow gas to enter the second cavity and that closes to prevent gas from exiting the second cavity via the second input port. Preferably, the input check valve and the output check valves comprise umbrella valves.

In one application of the pump, the second input port of the second pump stage is pneumatically coupled to a system to evacuate gas from the system to reduce the pressure in the system, and the first output port of the first pump stage discharges the gas at a higher pressure than the pressure in the system.

In preferred embodiments, the first rotor is positioned between a first cover and a second cover within the first cavity and rotates in a plane parallel to the first cover and the second cover. The first rotor has a first face proximate to and spaced apart from the first cover and has a second face proximate to and spaced apart from the second cover. Each of the first face and the second face of the rotor has a plurality of slots formed therein perpendicular to the face. The plurality of slots on each face functions as a respective labyrinth seal to reduce the flow of gas across each face between each face and the respective cover.

In preferred embodiments, the pump includes a third stage having a third trochoidal-shaped cavity having a third volume greater than the second volume. The third stage has a third input port and a third output port. A third rotor rotates eccentrically within the third cavity about a third cam. The third cam is also rotated by the common shaft. A second interconnection conduit couples the third output port to the second input port. Preferably, the pump further includes a fourth stage having a fourth trochoidal-shaped cavity having a fourth volume greater than the third volume. The fourth stage has a fourth input port and a fourth output port. A fourth rotor rotates eccentrically within the fourth cavity about a fourth cam. The fourth cam is also rotated by the common shaft. A third interconnection conduit couples the fourth output port to the third input port. In a preferred application of the four-stage pump, the fourth input port is coupled to a system from which gas is to be evacuated. The fourth pump stage draws gas from the system into the fourth cavity to reduce the pressure in the system to a system pressure and outputs the gas to the third stage via the third interconnection conduit at a fourth stage output pressure that is higher than the system pressure. The third pump stage increases the pressure of the gas from the fourth stage output pressure to a third stage output pressure and outputs the gas to the second stage via the second interconnection conduit. The second pump stage increases the pressure of the gas from the third stage output pressure to a second stage output pressure and outputs the gas to the first stage via the first interconnection conduit. The first pump stage increases the pressure of the gas from the second stage output pressure to atmospheric pressure and outputs the gas via the first output port.

In preferred embodiments of the pump, the first trochoidal-shaped cavity includes a first cavity lobe and a second cavity lobe. The first cavity lobe is coupled to the first input port. The second cavity lobe is coupled to the first output port. An internal interconnection passage has an inlet positioned in the first cavity lobe and has an outlet positioned in the second cavity lobe. The internal interconnection passage transfers gas from the first cavity lobe to the second cavity lobe when a vertex of the first rotor is positioned between the inlet and the outlet.

Another aspect of embodiments in accordance with the present invention is a pump that comprises a first stage and a second stage. The first stage comprises a first enclosure having a first inner cavity having a first volume. The first inner cavity is defined by a first inner surface with a trochoidal shape. A first circular cam has a first central axis and has a first eccentric axis offset from the first central axis. The first circular cam is mounted in the first cavity to rotate about the first eccentric axis. A first rotor is mounted to rotate about the first central axis of the first circular cam. The first rotor has a plurality of vertices that move along the first inner surface of the first inner cavity. The first stage further includes a first input port to enable gas to enter the first inner cavity and a first output port to enable gas to exit from the first inner cavity. The second stage comprises a second enclosure having a second inner cavity having a second volume. The second volume is greater than the first volume. The second inner cavity is defined by a second inner surface with a trochoidal shape. A second circular cam has a second central axis and has a second eccentric axis offset from the second central axis. The second circular cam is mounted in the second cam to rotate about the second eccentric axis. A second rotor is mounted to rotate about the second central axis of the second circular cam. The second rotor has a plurality of vertices that move along the second inner surface of the second inner cavity. The second stage includes a second input port to enable gas to enter the second inner cavity and a second output port to enable gas to exit from the second inner cavity. A common shaft rotates the first circular cam around the first eccentric axis and rotates the second circular cam around the second eccentric axis at an input rate. The first rotor rotates about the first circular cam at first rotation rate that is a first fixed fraction of the input rate. The second rotor rotates about the second circular cam at a second rotation rate that is a second fixed fraction of the input rate. An interconnection conduit couples the second output port to the first input port. Preferably, the first rotation rate and the second rotation rate are the same.

Another aspect of embodiments in accordance with the present invention is a four-stage vacuum pump. The four-stage vacuum pump comprises a first stage, a second stage, a third stage and a fourth stage. The first stage comprises a first trochoidal-shaped cavity having a first volume and having a first rotor that rotates eccentrically within the first cavity. The first stage receives a gas at an input pressure and outputs the gas at a second pressure higher than the input pressure. The second stage comprises a second trochoidal-shaped cavity having a second volume and having a second rotor that rotates eccentrically within the second cavity. The second stage receives the gas from the first stage at the second pressure and outputs the gas at a third pressure higher than the second pressure. The third stage comprises a third trochoidal-shaped cavity having a third volume and having a third rotor that rotates eccentrically within the third cavity. The third stage receives the gas from the second stage at the third pressure and outputs the gas at a fourth pressure higher than the third pressure. The fourth stage comprises a fourth trochoidal-shaped cavity having a fourth volume and having a fourth rotor that rotates eccentrically within the fourth cavity. The fourth stage receives the gas from the third stage at the fourth pressure and outputs the gas at an exhaust higher than the fourth pressure. A common shaft rotates first, second, third and fourth eccentric cams and the first, second, third and fourth rotors rotate about the respective first, second, third and fourth eccentric cams. Each stage has at least one intake phase and at least one exhaust phase. In a particularly preferred embodiment, the cams and rotors in the four stages are positioned at selected respective angular positions on the common shaft. The angular positions are selected such that the rotor in a stage receiving gas from another stage is in an intake phase when the stage providing the gas is in an exhaust phase

Another aspect of embodiments in accordance with the present invention is a method of lowering the pressure at an interface. In accordance with the method, a rotational force is applied to a common rotating shaft that is coupled to a first pump stage and at least a second pump stage. Each pump stage has a respective trochoidal-shaped chamber and has a respective rotor positioned in the chamber to rotate about a respective eccentric cam driven by the rotating shaft. The chamber in the first pump stage has a first volume. The chamber in the second pump stage has a second volume greater than the first volume. Gas is drawn into the second pump stage at an intake pressure, and gas is expelled from the second pump stage into the first pump stage at a second stage output pressure greater than the intake pressure. Gas is expelled from the first pump stage at a first stage output pressure greater than the second stage output pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and other aspects of this disclosure are described in detail below in connection with the accompanying drawing figures in which:

FIG. 1 illustrates a perspective view of a multi-stage vacuum pump having four stages driven by a common shaft connected to a single motor;

FIG. 2 illustrates an exploded perspective view of the vacuum pump of FIG. 1 looking in the direction of FIG. 1 to show the support base, the four interconnected stages, the drive motor and the drive coupler;

FIG. 3 illustrates an exploded perspective view of the vacuum pump of FIG. 1 similar to FIG. 2 but looking in the opposite direction from the direction of FIG. 2;

FIG. 4 illustrates a top view of the vacuum pump of FIG. 1;

FIG. 5 illustrates an exploded perspective view of the four pump stages of FIGS. 2 and 3 taken in the direction of FIG. 2;

FIG. 6 illustrates an exploded perspective view of the four pump stages of FIGS. 2 and 3 taken in the direction of FIG. 3;

FIG. 6A illustrates an elevational cross-sectional view of the exploded view of FIG. 6 taken along the lines 6A-6A in FIG. 6;

FIG. 7 illustrates an elevational cross-sectional view of the four pump stages, the coupler and a portion of the drive motor taken along the lines 7-7 in FIG. 4;

FIG. 8 illustrates an exploded perspective view of the first stage of the vacuum pump of FIGS. 2 and 3 in the direction of FIG. 2 showing the closed rear wall of the housing and showing the fixed gear, the rotating gear, the eccentric cam and the triangular rotor that fit within the housing;

FIG. 9 illustrates an exploded perspective view of the first stage of the vacuum pump of FIGS. 2 and 3 in the direction of FIG. 3 showing the open cavity of the housing and showing the fixed gear, the rotating ring gear, the eccentric cam and the triangular rotor that fit within the housing;

FIG. 10A illustrates an enlarged perspective view of the front face of the rotor of FIG. 9 showing the eccentric axis for the cam and showing the arcuate slots that form the front labyrinth seal;

FIG. 10B illustrates a perspective view of the rear face of the rotor of FIG. 8 showing the installation of the ring gear in the rotor, with the fixed spur gear shown for reference, and also showing the triangular slots at the vertices that form the rear labyrinth seal;

FIG. 10C illustrates an elevation view of the front face of the rotor showing the dimension R and the eccentricity e, which determine the trochoid shape of the cavity of the enclosure;

FIG. 11 illustrates an enlarged perspective view of the first pump stage of FIG. 6 with the rotor shown in phantom to show the relationship of the fixed gear, the rotating ring gear and the eccentric cam;

FIG. 12 illustrates a cross-sectional elevational view of the first pump stage of FIG. 11 taken along the lines 12-12 of FIG. 11 to show the input port, the inlet passage, the interconnecting passage, the outlet passage, the outlet port and the umbrella valve in the outlet port;

FIG. 13 illustrates an enlarged cross-sectional view of the output port and the output umbrella valve of FIG. 12 within the area bounded by the dashed arc 13 in FIG. 12 to show the outlet umbrella valve in the closed position to block reverse flow of gas into the first inner cavity;

FIG. 13A illustrates the enlarged cross-sectional view of FIG. 13 to show the outlet umbrella valve in the open position to allow flow of gas from the first inner cavity via the first output port;

FIG. 14 illustrates an exploded perspective view of the second stage of the vacuum pump of FIGS. 2 and 3 in the direction of FIG. 2;

FIG. 15 illustrates an exploded perspective view of the second stage of the vacuum pump of FIGS. 2 and 3 in the direction of FIG. 3;

FIG. 16 illustrates an exploded perspective view of the third stage of the vacuum pump of FIGS. 2 and 3 in the direction of FIG. 2;

FIG. 17 illustrates an exploded perspective view of the third stage of the vacuum pump of FIGS. 2 and 3 in the direction of FIG. 3;

FIG. 18 illustrates an exploded perspective view of the fourth stage of the vacuum pump of FIGS. 2 and 3 in the direction of FIG. 2;

FIG. 19 illustrates an exploded perspective view of the fourth stage of the vacuum pump of FIGS. 2 and 3 in the direction of FIG. 3;

FIG. 20 illustrates a cross-sectional elevational view of the fourth pump stage of FIG. 19 similar to the cross-sectional elevational view of the first pump stage of FIG. 12, which shows a similar outlet umbrella valve in the outlet port, and which further shows the inlet umbrella valve in the fourth input port;

FIG. 21 illustrates an enlarged cross-sectional view of the input port and the inlet umbrella valve of FIG. 20 within the area bounded by the dashed arc 21 in FIG. 20 to show the inlet umbrella valve in the closed position to block reverse flow of gas from the fourth inner cavity;

FIG. 21A illustrates the enlarged cross-sectional view of FIG. 21 to show the inlet umbrella valve in the open position to allow flow of gas into the fourth inner cavity via the fourth input port;

FIG. 22 illustrates an enlarged cross-sectional view of the output port and the output umbrella valve of FIG. 20 within the area bounded by the dashed arc 22 in FIG. 20 to show the outlet umbrella valve in the closed position to block reverse flow of gas into the fourth inner cavity;

FIG. 22A illustrates the enlarged cross-sectional view of FIG. 22 to show the outlet umbrella valve in the open position to allow flow of gas from the fourth inner cavity via the fourth output port; and

FIGS. 23A-23M illustrate cross-sectional elevation views of the first pump stage in accordance with the view of FIG. 12 to show the positions of the rotor and the internal gear of the first rotor with respect to the fixed spur gear as the first cam rotates clockwise about the common shaft in 90-degree increments and the first rotor rotates about the center of the first cam in 30-degree increments.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIGS. 1-7 illustrate a multi-stage vacuum pump 10 comprising a four-stage pump assembly 12 and a motor 14 mounted on a common platform (or base) 16. The motor receives power from a DC power source (not shown) via a power connection 18. The motor has an output shaft 20 that provides rotational power to the pump assembly via an output coupler 22. The output shaft and the output coupler rotate about a rotational axis 24.

The four-stage pump assembly 12 comprises a first pump stage 30, a second pump stage 32, a third pump stage 34 and a fourth pump stage 36. The first pump stage is an exhaust stage. The fourth pump stage is an intake stage. The second pump stage and the third pump stage are intermediate stages. In the illustrated embodiment, the fourth pump stage is mounted closest to the motor, and the first pump stage is mounted farthest from the motor; however, the positions of the pump stages can be varied in other embodiments.

The first pump stage 30 has an input port 40 and an output port 42. The second pump stage 32 has an input port 44 and an output port 46. The third pump stage 34 has an input port 48 and an output port 50. The fourth pump stage 36 has an input port 52 and an output port 54.

The output port 42 of the first pump stage 30 is coupled to the ambient environment or to an enclosure (not shown) at an ambient pressure via an exhaust conduit 60. The input port 40 of the first pump stage is coupled to the output port 46 of the second pump stage 32 by a first interconnection conduit 62. The input port 44 of the second pump stage is coupled to the output port 50 of the third pump stage 34 by a second interconnection conduit 64. The input port 48 of the third pump stage is coupled to the output port 54 of the fourth pump stage 36 by a third interconnection conduit 66. The input port 52 of the fourth pump stage is coupled to an enclosure (not shown) or to an exhaust port of another pump (not shown) by an intake conduit 68.

In an advantageous application of the multi-stage vacuum pump 10, the multi-stage vacuum pump is a “roughing” pump that is able to reduce the pressure at the intake port (e.g., the input port 52 of the fourth pump stage 36) to approximately 1 Torr. Thus, the pressure in an enclosure (not shown) coupled to the intake port can be reduced to that level. Alternatively, a high-vacuum pump (not shown) can be coupled between the enclosure and the multistage pump. The high-vacuum pump exhausts to the intake of the multistage pump at approximately 1 Torr and is thus able to reduce the pressure in the enclosure to a pressure below 1 Torr.

In the illustrated embodiment, the motor 14 advantageously comprises a GM9413-2 Lo-Cog® D C Gearmotor, which is commercially available from Pittman of Harleysville, Pa. The motor operates over a range of voltages and includes internal gearing (not shown) that couples the rotational energy to the output shaft 20. For example, in one embodiment, the motor is operated at approximately 24 volts and provides a rotational velocity of approximately 200 rpm on the output shaft 100 with a power requirement in a range of approximately 6 watts to approximately 8 watts.

As shown in FIGS. 5, 6, 6A and 7, the rotational energy of the motor 14 is coupled from the output shaft 20 to a pump shaft 100 of the four pump stages 30, 32, 34, 36 via the output coupler 22 to an inner coupler 102 and a shaft sleeve 104. The pump shaft extends from the fourth pump stage to the first pump stage. For reference, the end of the pump shaft at the fourth pump stage (closest to the motor) is designated the proximal end, and the end of the pump shaft at the first pump stage is designated the distal end. In the illustrated embodiment, the pump shaft has a rectangular cross section. More particularly, the pump shaft has a square cross section with each side having a width of 0.125 inch. The pump shaft comprises tool steel in the illustrated embodiment but may comprise alternative materials of suitable strength in other embodiments.

In the illustrated embodiment, the outer coupler 22 is coupled to the output shaft 20 of the motor 14 in a conventional manner using a set screw 106 or other suitable securing device. The inner coupler 102 is preferably friction fit to the shaft sleeve 104. The shaft sleeve is generally cylindrical and has a first cylindrical portion with a first outer diameter that is selected to fit within an inner diameter of the inner coupler. The shaft sleeve has a second outer diameter proximate the pump shaft 100. At least the second portion and preferably both the first portion and the second portion of the shaft sleeve surround a central bore 108 having a generally rectangular shape sized to receive the proximal end of the pump shaft.

The fourth pump stage 36 includes a front cover 120 that has a cylindrical protrusion 122 that extends from the center of the cover. The protrusion is hollow and has an inner diameter sized to be larger than the inner coupler 102 so that the inner coupler is able to rotate freely within the protrusion. The end of the protrusion is sealed so that the fourth pump stage is sealed when the front cover is secured to the fourth pump stage. The protrusion has an outer diameter that is smaller than an inner diameter of the outer coupler 22 so that when the outer coupler is centered over the protrusion, the outer coupler able to rotate freely around the outside of the protrusion. Preferably, the front cover comprises molded plastic or another suitable light weight, low cost material.

The outer coupler 22 and the inner coupler 102 preferably comprise a ferromagnetic material, such as, for example, a neodymium-iron-boron (Nb—Fe—B) alloy, a samarium-cobalt (Sm—Co) alloy, or the like. The outer coupler and the inner coupler are mounted coaxially so that the outer coupler operates as a driver and the inner coupler operates as a follower for a magnetic coupling. The protrusion 122 of the cover 120 serves as a sealing barrier between the two elements of the magnetic coupling system so that the pump is sealed. When the outer coupler is rotated by the motor 14, the inner coupler rotates at substantially the same rotational velocity. Thus, rotational energy is coupled to the pump shaft 100 without penetrating the cover. In alternative embodiments, other coupling systems may be used.

As shown in FIGS. 5 and 6, for example, the first pump stage 30 comprises a first housing 200. The second pump stage 32 comprises a second housing 202. The third pump stage 34 comprises a third housing 204. The fourth pump stage 36 comprises a fourth housing 206. Additional pump stages can be included along with corresponding housings. Preferably, the housings have similar shapes. For example, each housing has a respective outer wall 210, 212, 214, 216, having a generally oval-shaped outer surface, and having a respective inner perimeter surface 220, 222, 224, 226. The inner perimeter surfaces define respective hollow cavities 230, 232, 234, 236 having respective depths in the direction of the rotational axis 24. Each inner perimeter surface is formed to have a two-lobed epitrochoidal shape, which is described in more detail below. The outer walls have different lengths so that the depths of the respective cavities are different. For example, in the illustrated embodiment, the cavity of the first pump stage has a first depth of approximately 0.29 inch. The depth of the cavity of the second pump stage is approximately twice the depth of the cavity of the first pump stage or approximately 0.58 inch. The depth of the cavity of the third pump stage is approximately twice the depth of the cavity of the second pump stage or approximately 1.16 inches. The depth of the cavity of the fourth pump stage is approximately three times the depth of the cavity of the second pump stage or approximately 1.74 inches. Preferably, each housing comprises molded plastic to provide a pump housing having a light weight and a low cost.

The first housing 200 has a first rear cover 240. The second housing 202 has a second rear cover 242. The third housing 204 has a third rear cover 244. The fourth housing 206 has a fourth rear cover 246. Each rear cover has the same general oval shape as the respective outer walls 210, 212, 214, 216. The front cover 120 also preferably has the same general oval shape. Preferably, each cover comprises molded plastic similar to the plastic used for the housing.

The first rear cover 240 of the first pump stage 30 has a thickness of approximately 0.075 inch and has a central protrusion 250 having a depth of approximately 0.125 inch. As shown in FIG. 9, the central protrusion includes an internal circular recess 252.

As further shown in FIG. 9, the circular recess 252 receives the distal end of a first cylindrical shaft sleeve 260. As shown in FIGS. 15, 17 an 19, the second, third and fourth pump stages 32, 34, 26 include respective second, third and fourth cylindrical shaft sleeves 262, 264, 266. In the illustrated embodiment, each cylindrical shaft sleeve has a diameter of approximately 0.2188 inch. The length of each shaft sleeve is different for each pump stage. For example, the first shaft sleeve has a length of approximately 0.29 inch, the second shaft sleeve has a length of approximately 0.56 inch, the third shaft sleeve has a length of approximately 1.14 inches, and the fourth shaft sleeve has a length of approximately 1.73 inches. The shaft sleeves may advantageously comprise brass or may comprise a light weight, low cost molded plastic.

As shown in FIGS. 8 and 9 for the first cylindrical sleeve 260, in FIGS. 14 and 15 for the second cylindrical sleeve 262, in FIGS. 16 and 17 for the third cylindrical sleeve 264 and in FIGS. 18 and 19 for the fourth cylindrical sleeve 266, each cylindrical sleeve includes a central through-bore 268 having a rectangular cross-section. The central through-bores are sized to receive the pump shaft 100. In the preferred embodiment, the cross section of each through-bore is a square having sides with widths of approximately 0.1288 inch.

The second rear cover 242, the third rear cover 244 and the fourth rear cover 246 each have a thickness of approximately 0.06 inch. Each of the second, third and fourth rear covers has a respective circular central opening 272, 274, 276, to receive the respective cylindrical shaft sleeves 262, 264, 266. The openings are sized to receive the cylindrical sleeves without binding and with minimal passage of gas through the openings. For example, in the preferred embodiment, the openings have diameters of approximately 0.23 inch.

As shown in FIG. 6 and FIGS. 10A-10C, for example, the first pump stage 30 includes a first rotor 300 positioned within the first housing 200. The second pump stage 32, the third pump stage 34 and the fourth pump stage 36 include a second rotor 302, a third rotor 304 and a fourth rotor 306, respectively. In the illustrated embodiment, each rotor has a substantially similar shape, which is generally triangular with three equal sides S1, S2, S3 and three vertices (tips) V1, V2 and V3. As shown in FIG. 10C, a distance from the geometric center of the first rotor to each vertex is R. In the illustrated embodiment, the nominal value of the distance R is approximately 1 inch; however, the actual distance R is reduced by approximately 0.005 inch to a distance of 0.995 inch to provide a small clearance with the first inner perimeter surface 220 to allow the vertices to follow the first inner surface without contacting the surface. As shown in FIGS. 10A, 10B, 10C for the first rotor, the three sides of each rotor are not straight. Rather, each side is arcuate. For example, in the illustrated embodiment, each side has an arcuate radius of approximately 2.56 inches such that the midpoint of each arcuate side of the rotor between two vertices is offset from a straight line connecting the two vertices by approximately 0.149 inch. Preferably, each rotor is molded from a light weight, low cost plastic, and advantageously comprises a material similar to the material used for the housing and other molded plastic parts.

As further illustrated in FIGS. 6 and 10A-10C for the first rotor 300, each vertex V1, V2, V3 of each rotor is solid such that the vertex has an uninterrupted continuous contour. Unlike other rotary pumps, which have flexible or spring-loaded seals at each tip (or vertex) to span the tolerance distance between the tip and the inner wall of the pressure chamber, the rotors in the preferred embodiment do not include any movable or flexible seals at the vertices. Rather, as discussed below, each vertex is positioned within approximately 0.005 inch of the first inner perimeter surface 220, and each vertex maintains this close tolerance as the vertex moves within the first inner cavity 230 along a trochoidal path that corresponds to the trochoidal shape of the first inner perimeter surface. Thus, additional seals are not required. Since the vertices move close to the first inner perimeter surface without touching the surface, the vertices do not wear and no residue caused by wear is deposited in the first inner cavity or elsewhere in the first pump stage.

Each rotor has a thickness selected for the depth of the respective cavity. For example, the first rotor 300 has a thickness of approximately 0.28 inch. The second rotor 302 has a thickness slightly more than approximately twice the thickness of the first rotor or approximately 0.57 inch. The third rotor 304 has a thickness of slightly more than approximately twice the thickness of the second rotor or approximately 1.15 inches. The fourth rotor 306 has a thickness slightly more than approximately three times the thickness of the second rotor or approximately 1.73 inches.

The first rotor 300 has a first circular through-bore 310 that passes through the geometric center of the first rotor. The second rotor 302, the third rotor 304 and the fourth rotor 306 have respective second, third and fourth through-bores 312, 314, 316. The first rotor rotates about the perimeter of a first circular cam 320, which has a diameter corresponding to the diameter of the through-bore, and which has a length determined by the thickness of the rotor. The diameter of the through-bore of the first rotor and the diameter of the first cam have a close tolerance so that the first rotor rotates freely about the first cam without binding or wobbling. For example, in the illustrated embodiment, the diameter of the through-bore of the first rotor is slightly greater than approximately 0.63 inch, and the outer diameter of the first cam is slightly less than approximately 0.63 inch. In like manner, the respective second, third and fourth through-bores allow the second rotor, the third rotor and the fourth rotor to rotate about a second circular cam 322, a third circular cam 324 and a fourth circular cam 326, respectively. Each cam has a length selected for the respective rotor. For example, in the illustrated embodiment, the first cam has a length of approximately 0.15 inch, the second cam has a length of approximately 0.44 inch, the third cam has a length of approximately 1.02 inches and the fourth cam has a length of approximately 1.6 inches.

As shown in FIGS. 8, 9 and 10C for the first cam 320, each of the first cam 320, the second cam 322, the third cam 324 and the fourth cam 326 has a respective first axis 330 passing through the geometric center of the circular cam, which corresponds to the geometric center of the respective rotor 300, 302, 304, 306. Each cam has a respective second axis 332, which is offset from the first axis by a distance e (FIG. 10C), which is also referred to as the eccentricity of the cam. Each cam has a circular through-bore 334, which is centered on the second axis. The first cylindrical shaft sleeve 260 is positioned in the through-bore of the first cam and is secured therein. For example, in the illustrated embodiment, the outer diameter of the first shaft sleeve is selected to approximately 0.22 inch so that the first shaft sleeve fits snugly in the through-bore. The first cam is secured to the first shaft sleeve in a suitable manner so that first cam rotates with the first shaft sleeve and thus rotates with the common shaft 100. For example, the first cam is advantageously secured to the first shaft sleeve by sizing the first cam and the first shaft sleeve for a friction fit or a press fit. Alternatively or in addition, the first cam may be secured to the first shaft sleeve with a suitable adhesive. The second cylindrical shaft sleeve 262, the third cylindrical shaft sleeve 264 and the third cylindrical shaft sleeve 264 are secured within the respective cylindrical bores of the second cam, the third cam and the fourth cam in like manner. Each cam preferably comprises a molded light weight, low cost plastic material and is advantageously made of a similar material to the materials used for the other molded plastic parts.

As discussed in more detail below, when the pump stages are assembled, the respective second axis 332 of each cam 320, 322, 324, 326 is aligned with the pump axis 24. When the pump shaft 100 is rotated by the motor 14, each cam rotates about the second axis which causes the respective first axis 330 of each cam to move in a circle about the second axis. Thus, the center of each rotor 300, 302, 304, 306 rotates about the second axis and thus rotates about the pump shaft. As further discussed below, in the preferred embodiment, the components are selected and arranged so that each rotor rotates about the first axis of the respective cam by an angle θ as the cam rotates about the pump shaft (e.g., about the second axis) by an angle 3θ. Thus, each rotor will rotate one full turn about the respective first axis when the respective cam rotates three full turns about the second axis.

As shown in FIG. 9, the inside of the first rear cover 240 of the first housing 200 of the first pump stage 110 includes a first annular recess 350 centered about the circular recess 252 of the central protrusion 250. The annular recess is shallow and has a depth of approximately 0.025 inch and a diameter of approximately 0.75 inch. The perimeter of the annular recess has a plurality of inwardly pointing positioning teeth 352, which are sized and shaped to mate with the teeth of a spur gear 354. For example, in the illustrated embodiment, the four positioning teeth are positioned at 90-degree intervals about the perimeter of the annular recess.

In the illustrated embodiment, the spur gear 354 advantageously has 32 outwardly facing teeth that are equally spaced about the perimeter of the spur gear. The spur gear has a central bore 356. The spur gear has an outer diameter of approximately 0.71 inch and has a thickness of approximately 0.12 inch. In one embodiment, the spur gear advantageously comprises a G138 spur gear commercially available from Boston Gear of Quincy, Mass. Preferably, the spur gear comprises brass or another suitable material. The spur gear is centered in the annular recess 350 with the central bore of the spur gear concentric with the circular recess 252. The positioning teeth 352 assure that the spur gear is positioned in the annular recess with a known orientation (e.g., with a gap between adjacent teeth of the spur gear at 0 degrees, 90 degrees, 180 degrees and 270 degrees. The spur gear is secured to the inside of the first rear cover 240 by a suitable adhesive or another fastening system. The central bore of the spur gear is bored out from an original diameter to a diameter that closely matches the outer diameter of the first cylindrical shaft sleeve 260. For example, the central bore of the spur gear is advantageously 0.2188 inch in the illustrated embodiment. The central bore of the spur gear functions as a wear-resistant bearing surface for the first shaft sleeve so that the first shaft sleeve rotates freely and smoothly therein.

The inside of each of the second rear cover 242, the third rear cover 244 and the fourth rear cover 246 includes a corresponding annular recess (not shown) centered around the respective central openings 272, 274, 276. Each annular recess has the set of positioning teeth (not shown) to locate a respective 32-tooth spur gear 354 as described above. Each spur gear functions as a bearing surface for the respective shaft sleeve.

As illustrated in FIGS. 8 and 10B, the first rotor 300 has a rear face 400 positioned toward the first rear cover 240 of the first housing 210. As illustrated in FIGS. 9 and 10A, the first rotor has an opposing front face 402 directed away from the first rear cover. The rear face includes an annular recess 404 centered about the first through-bore 310. The annular recess in the rear face of the first rotor has a diameter of approximately 1.205 inches and has a depth of approximately 0.13 inch. The rotor has a plurality of mounting holes 406 (e.g., three holes) spaced equidistantly from and about the center. For example, the mounting holes have diameters of approximately 0.067 inch and are positioned 120 degrees apart at a radius of approximately 0.5635 inch. The mounting holes extend through the rotor to the front face. The mounting holes are surrounded by countersinks 408 on the front face.

As shown in FIGS. 8 and 10A, the annular recess 404 in the rear face of the first rotor 300 is sized to receive an internal gear 410. In the illustrated embodiment, the internal gear advantageously comprises a G632 internal gear commercially available from Boston Gear of Quincy, Mass. The internal gear advantageously comprises brass or another suitable material. The internal gear has 48 inwardly pointing teeth, has an outside diameter of approximately 1.5 inches and has a pitch diameter of approximately 1.0 inch. The outside diameter of the internal gear is machined to a diameter of 1.2 inches to fit snugly within the annular recess. The internal gear has a thickness of approximately 0.1275 inch. Three mounting holes 412 are formed in the internal gear equidistantly about the center (e.g., at 120-degree intervals) and are spaced approximately 0.5635 inch from the center of the internal gear to align with the mounting holes 406 in the first rotor. Each mounting hole in the internal gear has a diameter of approximately 0.47 inch and is threaded internally to receive a machine screw 414 that passes through the respective mounting hole in the rotor. Each mounting hole of the internal gear is aligned with a respective one of the inwardly pointing teeth so that the internal gear is positioned at a known angular position with respect to the vertices of the first rotor. When the internal gear is positioned in the annular recess, the face of the internal gear is recessed slightly with respect to the rear face of the first rotor.

The rear face 400 of the first rotor 300 includes a first V-shaped slot 420 and a second V-shaped slot 422 inset from each of the vertices. The front face 402 of the first rotor 300 includes a first arcuate slot 424 and a second arcuate slot 426, which are inset from the arcuate sides. For example, the two arcuate slots on the front face are generally continuous around the perimeter of the front face. The arcuate slots on the front face and the V-shaped slots on the rear face have depths of approximately 0.1 inch and widths of approximately 0.0422 inch. The slots function as labyrinth seals on the two faces of the rotor. In particular, the front and rear faces of the rotor are positioned in the first cavity 230 with a gap of approximately 0.005 inch between the rear face of the rotor and the back cover 240 of the first enclosure 200, and with a gap of approximately 0.005 inch between the front face of the rotor and the back cover 242 of the second enclosure 202. Gas moving across a face of the rotor in the narrow gap and encountering the slots will tend to expand into the slots, thus inhibiting the flow of gas across the faces, particularly in the vicinity of the vertices.

As shown in FIGS. 11 and 12, the first rotor 300 is mounted in the first cavity 230 of the first housing 200 with the shaft sleeve 260 positioned in the center bore 356 of the spur gear 354. Thus, the second axis 332 of the first cam 320 is aligned with the center of the first cavity and is also aligned with the rotational axis 118 of the pump shaft 100. As discussed above, the center of the first cam on the first axis 330 is offset from the center of the first cavity by the eccentricity distance e. Thus, the center of the internal gear 410 is offset from the center of the spur gear as shown.

The first rotor 300 is initially positioned in the first housing 200 with a gap between two teeth of the internal gear 410 fully engaged with a tooth of the spur gear 354 and with the vertices of the first rotor touching the inner perimeter surface 220 of the first housing. The first shaft sleeve 260 is positioned in the central bore 356 of the spur gear with the adjacent face of the first circular cam 320 resting on the face of the spur gear. The engagement of the internal gear of the first rotor with the fixed spur gear and the rotation of the first cam about the rotational axis of the pump shaft 100 causes the first rotor to rotate about the first cam at a rate determined by the number of teeth in the two gears. In particular, the ratio of the 48 teeth of the internal gear to the 32 teeth of the spur gear causes the first rotor to rotate about the first cam once for every three revolutions of the first cam about the rotational axis of the pump shaft. The other cams and rotors are installed in the respective housings of the other pump stages in like manner.

As discussed above, the first inner perimeter surface 220 of the first cavity 230 and the corresponding inner perimeter surfaces 222, 224, 226 of the other cavities have epitrochoidal shapes. The shape of the first inner perimeter surface is selected to correspond to the movement of the vertices of the first rotor 300 as the first rotor rotates in the first cavity. In particular, the shape of the first inner perimeter surface is determined by the distance R of the vertices from the center of the first rotor, by the eccentricity e of the center of the first rotor with respect to the center of the first cavity, and by the relative angular rotation rates of the first cam 320 and the first rotor.

For the illustrated embodiment, the first inner perimeter surface of the first cavity 230 has a two-lobed epitrochoidal shape in accordance with the following equations:

x=R·cos(θ)+e·cos(3θ)  (1)

y=R·sin(θ)+e·sin(3θ)  (2)

In Equations (1) and (2):

-   -   x is the horizontal distance from the center of the cavity 230         to a point on the inner perimeter surface 220;     -   y is the vertical distance from the center of the cavity to the         point on the inner perimeter surface;     -   R is the nominal distance from the center of the rotor 310 to         each tip of the rotor, which is approximately 1 inch, as         discussed above;     -   e is the eccentricity between first axis 330 and the second axis         332 of the first cam 320, as discussed above; and     -   θ is the angle of rotation of the first rotor about the first         axis of the cam, and 3θ is the angle of rotation of the cam         about the second axis. Both angles are measured with respect to         an initial position where the two axes and a tip of the rotor         are aligned horizontally. The angle 3θ of the cam is measured         with respect to the fixed second axis, but the angle θ is         measured with respect to the first axis, which rotates as the         cam rotates. The cam rotates at a rate that is three times the         rate of rotation of the rotor because of the relative number of         teeth of the internal gear 410 and the fixed spur gear 354.

As discussed above, the vertices V1, V2 V3 of the first rotor 300 rotate about the center of the first cam 320. As the first cam rotates about the rotational axis of the pump shaft, each vertex follows the inner perimeter surface at an offset distance of approximately 0.005 inch. Thus, each vertex maintains a substantially constant seal with respect to the inner perimeter surface without frictional contact and wear. No seals (e.g., flexible seals, spring-loaded vanes, or the like) are required in order to maintain the close tolerance.

When the first rotor 300 is positioned in the first cavity, a face of the first cam 320 rests on the exposed face of the spur gear 354. Thus, the face of the spur gear provides a bearing surface for the first cam. The length of the first cam and the thickness of the spur gear are selected so that the opposite face of the first cam is recessed from the second face 402 of the first rotor by a sufficient amount to allow a distal end of the second shaft sleeve 262 to penetrate a short distance into the first cavity 230. For example, in the illustrated embodiment, the opposite face of the first cam is recessed approximately 0.0425 inch from the second face of the first rotor to provide clearance for any portion of the second shaft sleeve that may protrude into the first cavity through the central opening 272 of the second rear cover 242 of the second housing 202.

As shown in FIGS. 14 and 15, the second pump stage 32 is assembled in similar manner to the first pump stage 30. As discussed above, the thickness of the second rotor 302 is approximately twice the thickness of the first rotor 300, and the thickness of the second cam 322 and the length of second cylindrical sleeve 262 are adjusted accordingly. The countersinks in the front face 402 of the second rotor are deeper so that machine screws of the same length can be used for both rotors. The slots in the rear face and the slots in the front face of the second rotor are also deeper than the corresponding slots in the first rotor. The remaining elements of the second rotor assembly are the same as the corresponding elements of the first rotor and are numbered accordingly.

FIGS. 16 and 17 illustrate the assembly of the components of the third pump stage 34, and FIGS. 18 and 19 illustrate the assembly of the fourth pump stage 36. As discussed above, the thickness of the third rotor 304 and the depth of the third cavity 234 for the third pump stage are approximately twice the thickness and depth of the second rotor and the second cavity. The thickness of the fourth rotor 306 and the depth of the fourth cavity 236 for the fourth pump stage are approximately three times the thickness and depth of the second rotor and the second cavity.

Each outer wall 210, 212, 214, 216 of the housings 200, 202, 204, 206 includes a plurality of bosses 500 spaced approximately equidistantly about the respective wall. Each boss includes a respective through-bore 502. The front cover 150 of the fourth pump stage 116 includes a corresponding plurality of ears 510 with respective through-bores 512. When the housings and the front cover are assembled, the through-bores in the bosses on the housings and the through-bores in the ears of the front cover are aligned to receive a corresponding plurality of fasteners (e.g., combinations of bolts 520 and nuts 522) to secure the four pump stages together.

When fully assembled, the rear cover 242 of the second pump stage 32 seals the front of the housing 200 of the first pump stage 30. The rear cover 244 of the third pump stage 34 seals the front of the housing 202 of the second pump stage. The rear cover 246 of the fourth pump stage 36 seals the front of the housing 204 of the third pump stage. The front cover 150 seals the front of the housing 206 of the fourth pump stage and thus seals the overall four-stage pump assembly 12.

As further illustrated in FIGS. 9, 15, 17 and 19, the front face of each housing 200, 202, 204, 206 includes an oval-shaped groove 530 inset from the outer wall. Each groove receives a conventional O-ring gasket (not shown) to form a respective gas-tight seal between the cover and the face. As discussed above, the grooves 420, 422, 424, 426 in the rotors 300, 302, 304, 306 function as labyrinth seals between the rear and front faces 400, 402 of the rotors and the inside surfaces of the respective covers.

When the four pump stages 30, 32, 34, 36 are assembled, the respective rotors and cams in the pump stages may be aligned; however, in the illustrated embodiment, the cam in each successive stage is advantageously offset by a selected number of degrees from the cam in the preceding stage. For example, as shown in FIG. 6, each successive cam is offset by 90 degrees from the cam in the preceding stage. In particular, the fourth cam 326 in the fourth pump (intake) stage 36 is positioned in the initial position discussed above (e.g., at the zero-degree location). In the illustrated initial position, the two axes and a tip (vertex) of the fourth rotor 306 are aligned horizontally, and the respective first (center) axis 330 of the fourth cam is positioned to the right of the second (pump) axis 332. Accordingly, one vertex of the fourth rotor is pointed toward the 3 o'clock position when looking at the face of the fourth pump housing 206. (As used herein, the terms “initial position” or “initially” are used to indicate a relative angular location for the cams and rotors at a particular time while the pump is operating. The terms are used to provide a reference for discussion and are not intended to indicate actual starting positions for the rotors.)

The third cam 324 in the third stage 34 lags the fourth cam by 90 degrees. Thus, in the initial position shown in FIG. 6, the two axes of the third cam are aligned vertically, and the respective first (center) axis of the third cam is positioned above the second (pump) axis. One vertex of the third rotor 304 is pointed downward toward the 6 o'clock position.

The second cam 324 in the second pump stage 34 lags the third cam by 90 degrees. Thus, in the initial position shown in FIG. 6, the two axes of the third cam are aligned horizontally, and the respective first (center) axis of the second cam is positioned to the left of the second (pump) axis. Accordingly, the initial position of the second cam is in the opposite direction from the initial position of the fourth cam. One vertex of the second rotor 302 is pointing toward the 9 o'clock position.

The first cam 320 in the first pump (output) stage 30 lags the second cam by 90 degrees. Thus, in the initial position shown in FIG. 6, the respective first (center) axis of the first cam is vertically aligned with and is positioned below the second (pump) axis. One vertex of the first rotor 300 is pointed directly upward toward the 12 o'clock position. The advantages to the preferred alignment illustrated in FIG. 6 are discussed below following the descriptions of FIGS. 23A-23M. Since the cams have different sizes and thus have different masses, counterweights (not shown) may be used to offset the differences in masses if needed to reduce vibration.

As illustrated FIGS. 8, 9, 12 and 14-20, each of the respective output ports 42, 46, 50 and 54 of the four pump stages 30, 32, 34, 36 includes an output valve seat 600. As shown in FIGS. 18-20, the fourth input port 52 of the fourth pump stage includes an input valve seat 602. In an alternative embodiment (not shown), the other three input ports may also include an input valve seat. As shown, for example, in FIGS. 8 and 9, each valve seat is formed as a circular disk having a plurality of passages (e.g., four passages) 610 spaced about a central mounting hole 612. The valve seat advantageously comprises brass, plastic or another suitable material. In the illustrated embodiment, the valve seat has a diameter of approximately 0.375 inch and has a thickness of approximately 0.08 inch.

The central mounting hole in the input valve seat of each output port and the input port has a diameter of approximately 0.06 inch and is sized to receive the stem 622 of a conventional umbrella valve 620. The stem is stretched to insert the stem in the mounting hole. After insertion, the stem enlarges to retain the stem in the mounting hole. The canopy portion of the umbrella valve is sized to cover the passages, which are centered approximately 0.08 inch from the center of the valve seat and which have respective diameters of approximately 0.05 inch. Accordingly, an umbrella valve having a canopy with a diameter of at least 0.22 inch is adequate to cover the passages. For example, the umbrella valve advantageously comprises a UM 070.002 umbrella valve commercially available from MiniValve International of Oldenzaal, The Netherlands. Similar umbrella valves or other suitable valves from other manufacturers may also be advantageously used. The umbrella valves advantageously require only a relatively small pressure differential to open and allow gas to pass through the valve in the forward direction, but close securely when the pressure differential is insufficient or in the reverse direction.

The umbrella valve 620 in each output port 42, 46, 50, 54 is mounted with the stem 622 of the umbrella valve pointed downward (toward the hollow cavity 320) so that the flexible canopy of the umbrella valve is on the side of the valve seat facing away from the respective hollow cavity 230, 232, 234, 236. The umbrella valve in the fourth input port 52 is mounted with the stem pointed upward away from the fourth hollow cavity so that the flexible canopy portion of the umbrella valve is positioned between the input valve seat and the fourth hollow cavity.

The valve seats 600 are secured in the respective output ports 42, 46, 50, 54 and the fourth input port 52 using a suitable adhesive or other type of fastening system. Each of the input port and the output ports may include a ledge to assist in aligning the respective disk in the respective port.

As illustrated in FIGS. 13 and 13A, the umbrella valve 620 in the first output port 42 of the first pump stage 30 opens to permit gas flow out of the hollow cavity 230 when the pressure in the hollow cavity is sufficiently greater than the pressure on the exterior side to the first output port. The umbrella valve in the first output port closes when the difference between the pressures on the two sides of the umbrella valve is insufficient to open the umbrella valve. In particular, the umbrella valve in the first output port prevents reverse gas flow into the hollow cavity through the first output port. The umbrella valves in the other output ports 46, 50 and 54 operate in a similar manner for the other pump stages 32, 34, 36. For example, the umbrella valve in the fourth output port is shown in FIGS. 22 and 22A. Since the valves in the fourth output port, the third output port and the second output port are in the pneumatic paths coupled to the third input port 48, the second input port 44 and the first input port 40, respectively, valves are not required for the third, second, and first input ports.

As illustrated in FIGS. 21 and 21A, the umbrella valve 620 in the fourth input port 52 is positioned to open and permit gas flow into the fourth hollow cavity 236 when the pressure in the hollow cavity is sufficiently less than the pressure on the exterior side of the fourth port. The umbrella valve in the fourth input port closes when the difference between the pressures on the two sides of the umbrella valve is insufficient to open the umbrella valve. In particular, the umbrella valve in the input port prevents reverse gas flow out of the fourth hollow cavity via the first input port.

As shown in the cross-sectional illustration in FIG. 12, an input passage 650 couples the first input port 40 to an upper portion of a first lobe 652 of the first hollow cavity 230. As shown in FIG. 4, the input passage has an elongated oval cross section with a longer dimension of approximately 0.158 inch and a shorter dimension of approximately 0.02 inch. As further illustrated in FIG. 12, an output passage 654 having a similar cross section couples the first output port 42 to an upper portion of a second lobe 656 of the first hollow cavity. The first lobe and the second lobe are separated by a vertical central axis 658, which passes through the center of the first hollow cavity. The input passage and the output passage penetrate the inner perimeter wall 220 of the first hollow cavity at locations that are located approximately equidistantly from the vertical central axis.

A lower portion of the first lobe is connected to a lower portion of the second lobe by an interconnection passage 660 having a cross section with a shape and size similar to the shape and size of the cross sections of the input passage and the output passage. An inlet end 662 and an outlet end 664 of the interconnection passage penetrate the inner perimeter wall at respective locations. The location of the inlet end is closer to the central vertical axis than the location of the outlet end. As illustrated in FIG. 12, the interconnection passage is preferably formed entirely within the outer wall 210 of the first housing 200. In alternative embodiments (not shown), the interconnection passage can be formed as two passages through the outer wall and interconnected by external conduits.

The gear ratio between the 32 teeth of the stationary spur gear 354 and the 48 teeth of the rotating internal gear 410 causes the first rotor 300 to rotate about the first cam 320 once for every three revolutions of the first cam about the center of the cavity 230. The other cams and rotors operate in like manner. The rotation of the fourth rotor is illustrated in FIG. 23A-FIG. 23M, which show the motion of the first cam in one-quarter turn (45-degree) increments. In particular, the drawings shown the positions of the three sides S1, S2, S3 and the three vertices V1, V2, V3 of the rotor at 90-degree rotational increments of the first cam, which correspond to 30-degree rotational increments of the first rotor about the center of the first cam.

FIG. 23A illustrates the first circular cam 320 in a starting position wherein the center of the cam (indicated by the end of the axis 330) is directly to the right of rotational axis of the shaft (indicated by the end of the axis 332). The first vertex V1 of the first rotor 300 is positioned to the right of the cam center in FIG. 23A and is positioned proximate to the first inner perimeter surface 220 at the midpoint of the first lobe 652. In particular, with the center of the first cavity defined as x=0, y=0, the vertex V1 is located at a point x=(R+e), y=0, but is offset from that point by a distance of approximately 0.005 inch. The second vertex V2 is positioned 120 degrees counterclockwise from the first vertex V1. The third vertex V3 is positioned 120 degrees counterclockwise from the second vertex V2. The vertices V2 and V3 are also spaced apart from the first inner perimeter surface by approximately 0.005 inch. The first side S1 is defined between the vertex V1 and the vertex V2. The second side S2 is defined between the vertex V2 and the vertex V3. The third side S3 is defined between the vertex V3 and the vertex V1. The following paragraphs describe a complete rotation of the first rotor from the starting position shown in FIG. 23A back to the starting position in FIG. 23M.

As illustrated in FIG. 23A, a first chamber C1A is formed in the first lobe 652 between the side S1 of the rotor 300 and the inner perimeter surface 220. The volume of the chamber C1A is increasing, which causes gas to be drawn into the volume C1A from the first input port 40 via the input passage 650. A chamber is also present between the side S2 and the inner perimeter surface, and a chamber is also present between the side S3 and the inner perimeter surface. The other chambers are discussed below. Note that a particular side of the rotor forms different chambers throughout a complete cycle of the rotor.

In FIG. 23B, the first circular cam 320 has rotated by approximately 90 degrees clockwise from the position shown in FIG. 23A. The interaction between the internal gear 410 and the spur gear 354 causes the first rotor 300 to rotate by 30 degrees clockwise with respect to the center of the first cam. The combined effects of the two rotations cause the vertices V1, V2 and V3 to follow the inner perimeter surface 220 in the clockwise direction. In particular, the vertex V1 is located proximate to a point on the first inner perimeter surface defined by:

x=R·cos(30°)+e·cos(90°)

y=R·sin(30°)+e·sin(90°)

As discussed above, the vertex V1 is spaced apart from this point by approximately 0.005 inch. With respect to the side S1 between the vertex V1 and the vertex V2, the effective clockwise rotation of the rotor enlarges the volume of the chamber C1A so that gas continues to be drawn into the chamber C1A from the first input port 40 via the input passage 650.

In FIG. 23C, the first circular cam 320 has rotated another 90 degrees clockwise, and the first rotor 300 has rotated another 30 degrees clockwise with respect to the center of the first cam. The vertex V1 has moved further clockwise along the inner perimeter surface 220 to a location just before the inlet end 662 of the interconnection passage 660. In particular, the vertex V1 is located proximate to and spaced apart by approximately 0.005 inch from a point on the inner perimeter surface defined by:

x=R·cos(60°)+e·cos(180°)

y=R·sin(60°)+e·sin(180°)

At this rotational location, the volume of the chamber C1A has reached a maximum volume and will start to decrease with further rotation. Note that a chamber C1B has formed primarily in the second lobe 656 between the side S3 and the inner perimeter surface proximate the outlet end 664 of the interconnection passage 660. The volume of the chamber C1B is increasing as the rotor continues to rotate. In FIG. 23C, the inlet end 662 of the interconnection passage has not yet opened to the chamber C1A, and the chamber C1B is not yet pneumatically coupled to the chamber C1A.

In FIG. 23D, the first circular cam 320 has rotated another 90 degrees clockwise, and the first rotor 300 has rotated another 30 degrees clockwise with respect to the center of the first cam. The vertex V1 has moved further clockwise along the inner perimeter surface 220 to a location past the opening to the inlet end 662 of the interconnection passage 660. In particular, the vertex V1 is located proximate to and spaced apart by approximately 0.005 inch from a point on the inner perimeter surface defined by:

x=R·cos(90°)+e·cos(270°)

y=R·sin(90°)+e·sin(270°)

Thus, the chamber C1B is pneumatically coupled to the chamber C1A to form a composite chamber having the combined volumes of the two chambers. The lower pressure resulting from the effective enlargement of the combined chambers causes additional gas to be drawn into the combined chambers C1A and C1B from the first input port 40 via the input passage 650. In FIG. 23D, the vertex V2 has moved along the inner perimeter surface to a location just prior to reaching the input passage 650.

In FIG. 23E, the first circular cam 320 has rotated another 90 degrees clockwise to the original starting position of the first circular cam. The first rotor 300 has rotated another 30 degrees clockwise with respect to the center of the first cam. Although the first rotor appears to be in the original starting location, the vertex V1 has rotated 120 degrees clockwise with respect to the original position of the rotor when referenced to the center of the cam. The vertex V1 has moved further along the inner perimeter surface 220 to a location approximately midway between the inlet end 662 and the outlet end 664 of the interconnection passage 660. In particular, the vertex V1 is located proximate to and spaced apart by approximately 0.005 inch from a point on the inner perimeter surface defined by:

x=R·cos(120°)+e·cos(360°)=R·cos(120°)+e·cos(0°)

y=R·sin(120°)+e·sin(360°)=R·sin(120°)+e·sin(0°)

The vertex V2 has moved along the inner perimeter surface to the location originally occupied by the vertex V1 in FIG. 23A. The volume of the chamber C1A between the side S1 and the inner perimeter surface has decreased substantially and the volume of the chamber C1B between the side S3 and the first inner perimeter surface has reached a maximum volume and will decrease with further rotation. The vertex V3 has moved past the opening of the output passage 654. Thus, the decreasing total volume of the two chambers C1A and C1B causes the gas in the two chambers to be forced out of the first output port 42 via the output passage 654 and the open umbrella valve 620. In the meantime, a new chamber C2A has formed between the side S2 of the rotor and the inner perimeter surface. Gas is drawn into the chamber C2A from the first input port 40 via the input passage 650.

In FIG. 23F, the first circular cam 320 has rotated another 90 degrees clockwise, and the first rotor 300 has rotated another 30 degrees clockwise with respect to the center of the first cam. The vertex V1 has moved to a location just before the outlet end 664 of the interconnection passage 660. In particular, the vertex V1 is located proximate to and spaced apart by approximately 0.005 inch from a point on the inner perimeter surface defined by:

x=R·cos(150°)+e·cos(90°)

y=R·sin(150°)+e·sin(90°)

The volume of the chamber C1A has decreased to an insignificant amount just prior to being uncoupled from the chamber C1B. The volume of the chamber C1B continues to decrease to expel gas from the first output port 42 via the output passage 654 and the open umbrella valve 620. The volume of the chamber C2A proximate the side S2 continues to increase to cause additional gas to be drawn into the chamber C2A.

In FIG. 23G, the first circular cam 320 has rotated another 90 degrees clockwise, and the first rotor 300 has rotated another 30 degrees clockwise with respect to the center of the first cam. The vertex V1 has moved further clockwise along the inner perimeter surface 220. In particular, the vertex V1 is located proximate to and spaced apart by approximately 0.005 inch from a point on the inner perimeter surface defined by:

x=R·cos(180°)+e·cos(180°)

y=R·sin(180°)+e·sin(180°)

The volume of the chamber C1B has continued to decrease, which expels gas from the chamber C1B via the output passage 654 and the output port 42. The vertex V2 has moved to a location just before the inlet end 662 of the interconnection passage 660. At this rotational location, the volume of the chamber C2A has reached a maximum volume and will start to decrease with further rotation. A chamber C2B has formed between the side S1 and the inner perimeter surface proximate the outlet end 664 of the interconnection passage 660. The volume of the chamber C2B is increasing as the rotor continues to rotate. In FIG. 23G, the inlet end 662 of the interconnection passage has not yet opened to the chamber C2A, and the chamber C2B is not yet pneumatically coupled to the chamber C2A.

In FIG. 23H, the first circular cam 320 has rotated another 90 degrees clockwise, and the first rotor 300 has rotated another 30 degrees clockwise with respect to the center of the first cam. The vertex V1 has moved further clockwise along the inner perimeter surface 220 to a location just before the opening of the output passage 654 to the output port 42. In particular, the vertex V1 is located proximate to and spaced apart by approximately 0.005 inch from a point on the inner perimeter surface defined by:

x=R·cos(210°)+e·cos(270°)

y=R·sin(210°)+e·sin(270°)

The volume of the chamber C1B has decreased to an insignificant volume such that most of the gas in the chamber C1B has been expelled. The vertex V2 has moved past the opening to the inlet end 662 of the interconnection passage 660. Thus, the chamber C2B is pneumatically coupled to the chamber C2A to form a composite chamber having the combined volumes of the two chambers. The lower pressure resulting from the effective enlargement of the combined chambers causes additional gas to be drawn into the combined chambers C2A and C2B through the input passage 650. In FIG. 23H, the vertex V3 has moved along the inner perimeter surface to a location just prior to reaching the input passage 650.

In FIG. 23I, the first circular cam 320 has rotated another 90 degrees clockwise to the original starting position of the first circular cam. The first rotor 300 has rotated another 30 degrees clockwise with respect to the center of the first cam. The vertex V1 has effectively rotated 240 degrees clockwise with respect to the original position of the rotor when referenced to the center of the cam. In particular, the vertex V1 is located proximate to and spaced apart by approximately 0.005 inch from a point on the inner perimeter surface defined by:

x=R·cos(240°)+e·cos(720°)=R·cos(240°)+e·cos(0°)

y=R·sin(240°)+e·sin(720°)=R·sin(240°)+e·sin(0°)

The vertex V2 has moved further along the inner perimeter surface 220 to a location approximately midway between the inlet end 662 and the outlet end 664 of the interconnection passage 660. The volume of the chamber C2A between the side S2 and the inner perimeter surface has decreased substantially and the volume of the chamber C2B between the side S1 and the first inner perimeter surface has reached a maximum volume and will decrease with further rotation. The vertex V1 has moved past the opening of the output passage 654. Thus, the decreasing total volume of the two chambers C2A and C2B causes the gas in the two chambers to be forced out of the first output port 42 via the output passage 654 and the open umbrella valve 620. In FIG. 23I, a new chamber C3A has formed between the side S3 of the rotor and the inner perimeter surface. Gas is drawn into the chamber C3A from the first input port 40 via the input passage 650.

In FIG. 23J, the first circular cam 320 has rotated another 90 degrees clockwise, and the first rotor 300 has rotated another 30 degrees clockwise with respect to the center of the first cam. In particular, the vertex V1 is located proximate to and spaced apart by approximately 0.005 inch from a point on the inner perimeter surface defined by:

x=R·cos(270°)+e·cos(90°)

y=R·sin(270°)+e·sin(90°)

The vertex V2 has moved to a location just before the outlet end 664 of the interconnection passage 660. The volume of the chamber C2A has decreased to an insignificant amount just prior to being uncoupled from the chamber C2B. The volume of the chamber C2B continues to decrease to expel gas from the first output port 42 via the output passage 654 and the open umbrella valve 620. The volume of the chamber C3A proximate the side S3 continues to increase to cause additional gas to be drawn into the chamber C3A.

In FIG. 23K, the first circular cam 320 has rotated another 90 degrees clockwise, and the first rotor 300 has rotated another 30 degrees clockwise with respect to the center of the first cam. In particular, the vertex V1 is located proximate to and spaced apart by approximately 0.005 inch from a point on the inner perimeter surface defined by:

x=R·cos(300°)+e·cos(180°)

y=R·sin(300°)+e·sin(180°)

The vertex V2 has moved further clockwise along the inner perimeter surface 220 to cause the volume of the chamber C2B to continue to decrease, which expels gas from the chamber C2B via the output passage 654. The vertex V3 has moved to a location just before the inlet end 662 of the interconnection passage 660. At this rotational location, the volume of the chamber C3A has reached a maximum volume and will start to decrease with further rotation. A chamber C3B has formed between the side S2 and the inner perimeter surface proximate the outlet end 664 of the interconnection passage 660. The volume of the chamber C3B is increasing as the rotor continues to rotate. In FIG. 23K, the inlet end 662 of the interconnection passage has not yet opened to the chamber C3A, and the chamber C3B is not yet pneumatically coupled to the chamber C3A.

In FIG. 23L, the first circular cam 320 has rotated another 90 degrees clockwise, and the first rotor 300 has rotated another 30 degrees clockwise with respect to the center of the first cam. In particular, the vertex V1 is located proximate to and spaced apart by approximately 0.005 inch from a point on the inner perimeter surface defined by:

x=R·cos(330°)+e·cos(270°)

y=R·sin(330°)+e·sin(270°)

The vertex V2 has moved further clockwise along the inner perimeter surface 220 to a location just before the opening of the output passage 654 to the output port 42. The volume of the chamber C2B has decreased to an insignificant volume such that most of the gas in the chamber C2B has been expelled. The vertex V3 has moved past the opening to the inlet end 662 of the interconnection passage 660. Thus, the chamber C3B is pneumatically coupled to the chamber C3A to form a composite chamber having the combined volumes of the two chambers. The lower pressure resulting from the effective enlargement of the combined chambers causes additional gas to be drawn into the combined chambers C3A and C3B through the input passage 650. In FIG. 23L, the vertex V1 has moved along the inner perimeter surface to a location just prior to reaching the input passage 650.

In FIG. 23M, the first circular cam 320 has rotated another 90 degrees clockwise, and the first rotor 300 has rotated another 30 degrees clockwise with respect to the center of the first cam. In particular, the vertex V1 is located proximate to and spaced apart by approximately 0.005 inch from a point on the inner perimeter surface defined by:

x=R·cos(360°)+e·cos(1080°)=R·cos(0°)+e·cos(0°)

y=R·sin(360°)+e·sin(1080°)=R·sin(0°)+e·sin(0°)

Thus, the first rotor has effectively rotated clockwise such that the vertex V1 has moved along the first inner perimeter surface 220 in the first hollow cavity 230 to the original starting position to the right of the center of the first hollow cavity. The vertex V3 has moved further along the inner perimeter surface 220 to a location approximately midway between the inlet end 662 and the outlet end 664 of the interconnection passage 660. The volume of the chamber C3A between the side S3 and the inner perimeter surface has decreased substantially and the volume of the chamber C3B between the side S2 and the first inner perimeter surface has reached a maximum volume and will decrease with further rotation. The vertex V2 has moved past the opening of the output passage 654. Thus, the decreasing total volume of the two chambers C3A and C3B causes the gas in the two chambers to be forced out of the first output port 42 via the output passage 654 and the open umbrella valve 620. In the meantime, the original chamber C1A has again formed between the side S1 of the rotor and the inner perimeter surface. Gas is drawn into the chamber C1A from the first input port 40 via the input passage 650.

As described above, the first rotor 300 rotates once (θ=360°) about the first circular cam 320 for each three revolutions (θ=1080°) of the cam about the pump shaft 100. During each complete revolution of the first rotor, the chamber formed by each side of the first rotor varies in volume from a minimum to a maximum and back to a minimum in each of the two lobes of the first inner cavity 320. Each chamber participates in two expansion/intake strokes and two compression/exhaust strokes. The three sides of the rotor operate together to cause the first pump stage 110 to produce three intake strokes per revolution of the rotor.

The respective circular cams 322, 324, 326 and rotors 302, 304, 306 in the second pump stage 112, the third pump stage 114 and the fourth pump stage 116 operate in the same manner to draw in gas through the respective input port and to force gas out through the respective output port in three intake strokes and three exhaust strokes.

As discussed above with respect to FIG. 6, in certain preferred embodiments, the four-stage pump is advantageously assembled so that the cam in each successive stage lags the cam in the preceding stage by 90 degrees. Thus, in the illustrated example of FIG. 6, the fourth rotor 306 and the fourth cam 326 in the fourth pump (intake) stage 36 are shown positioned as in FIGS. 23A, 23E, 23I and 23M. The respective first (center) axis 330 of the fourth cam is horizontally aligned with and is positioned to the right of the second (pump) axis 332. One vertex of the fourth rotor points towards the 0-degree position (e.g., the 3 o'clock position). Accordingly, the side of the rotor opposite the vertex in the 3 o'clock position forms a chamber in the left portion of the fourth cavity 236 between a leading (upper left) vertex and a trailing (lower left) vertex. The leading vertex has just passed the respective output passage 654 (FIG. 12) to couple the left chamber to the output passage. As the fourth rotor continues to rotate clockwise from the position shown in FIG. 6, gas is forced from the chamber through the output passage to the output port 54. At the same time, a chamber formed in the upper right portion of the fourth cavity is positioned to draw in gas from a source (not shown) via the fourth input port 52 and the respective input passage 650.

The third cam 324 and the third rotor 304 in the third pump stage 34 are initially positioned as shown in FIGS. 23D, 23H and 23L. The respective first (center) axis of the third cam is aligned vertically with and is positioned above the second (pump) axis. One vertex of the third rotor is pointing downward toward the 6 o'clock position. Accordingly, the side of the third rotor opposite the downwardly pointing vertex forms a small chamber against the top of the third cavity 236 between a respective leading (upper right) vertex and trailing (upper left) vertex. The upper chamber has just completed expelling gas outward through the respective output passage and the third output port 50. The upper left trailing vertex of the upper chamber has just passed the output passage to decouple the upper chamber from the third output port. The leading vertex is just passing the respective input passage to couple the upper chamber to the third input port 48. As the third cam and the third rotor turn further clockwise, the volume of the upper chamber increases to receive the gas expelled by the contemporaneous exhaust cycle of the fourth cam 326 and the fourth rotor 306 in the fourth pump stage 36. The trailing vertex for the upper chamber is also the leading vertex for a chamber in the left portion of the third cavity. As that vertex decouples the upper chamber from the output passage, the vertex couples the left chamber to the output passage and to the third output port to begin the exhaust cycle for the left chamber.

The second cam 322 and the second rotor 302 in the second pump stage 32 are initially positioned as shown in FIGS. 23C, 23G and 23K. The respective first (center) axis of the second cam is aligned horizontally with and is positioned to the left of the second (pump) axis. One vertex of the second rotor is pointing to the left toward the 9 o'clock position. Accordingly, the vertex is the trailing vertex for a chamber at the upper left, which is exposed to the respective output passage and is thus coupled to the second output port 46. In the illustrated position, the upper left chamber is nearing the end of an exhaust cycle. At the same time, a chamber in the right portion of the second cavity 234 between the other two vertices is receiving the last portion of the gas expelled by the third pump stage 34 via the second input port 44 and the respective input passage. As the second cam and the second rotor turn further clockwise, the upper left chamber expels the gas to complete the exhaust cycle. At the same time, the right chamber and a newly formed lower left chamber begin a new exhaust cycle.

The first cam 320 and the first rotor 300 in the first pump stage 30 are initially positioned as shown in FIGS. 23B, 23F and 23J. The respective first (center) axis of the first cam is aligned vertically with and is positioned below the second (pump) axis. One vertex of the first rotor is pointing upward toward the 12 o'clock position. Accordingly, that vertex is the trailing vertex for an intake chamber in the right portion of the first cavity 230. The same vertex is the leading vertex for an exhaust chamber in the left portion of the first cavity. The intake chamber is coupled to the first input port 40 via the respective input passage to receive gas expelled by the second pump stage 32. The exhaust chamber expels gas via the respective output passage and the first output port 42.

As the pump shaft 100 rotates through three complete revolutions, each of the pump stages 30, 32, 34, 36 passes through the cycles shown in FIGS. 23A-23M in a synchronous manner so that each earlier (larger volume) pump stage expels gas to the next (smaller volume) pump stage when the next pump stage is at a phase in which a chamber is formed and is coupled to the respective input port to receive the gas. By assembling the pump stages with the rotors phased in the manner shown in FIG. 6 to operate in the above-described manner, the rotors in the four pump stages transfer gas efficiently from the intake (fourth) stage to the exhaust (first) stage.

In an exemplary operation, the fourth input port 52 of the fourth pump stage 36 is coupled to a system to be evacuated or to the output of a high-vacuum pump. The relatively large volume of the fourth cavity 236 creates a large low-pressure volume that draws in the gas molecules from the system at pressures as low as approximately 1 Torr. The fourth rotor 306 operates as described above to compress the gas within the fourth cavity and expel the gas at a higher pressure via the fourth output port 54. The gas expelled from the fourth stage is drawn into the third cavity 234 of the third pump stage 34 via the third input port 48. The third cavity advantageously has a smaller volume than the fourth cavity since the gas molecules are compressed to a smaller volume. The third rotor 304 further compresses the gas within the third cavity and expels the compressed gas via the third output port 50. The gas expelled from the third stage is drawn into the second cavity 232 of the second pump stage 32 via the second input port 44. The second cavity advantageously has a smaller volume than the third cavity since the gas molecules are compressed to a smaller volume by the third stage. The second rotor 302 further compresses the gas within the second cavity and expels the compressed gas via the second output port 44. The gas expelled from the second stage is drawn into the first cavity 230 of the first pump stage 30 via the first input port 40. The first cavity advantageously has a smaller volume than the second cavity since the gas molecules are compressed to a smaller volume by the second stage. The first rotor 30 further compresses the gas within the first cavity and expels the compressed gas to the atmosphere via the first output port 42.

If additional pump stages are needed to provide a desired range of pumping pressures, the additional stages can be inserted between the front cover 120 and the fourth pump stage 36, for example. Additional pump stages can also be located between the illustrated pump stages since each pump stage except the first pump stage has the same construction other than the depths of the respective cavities and the lengths of the respective shaft sleeves, cams and rotors. The common pump shaft 100 can be lengthened to accommodate the additional stages.

In the illustrated embodiments, the pump stages are positioned in the order of the respective sizes; however, the stages can be positioned in alternative orders with appropriate modifications to the interconnections. Furthermore, although the pump stages operate serially in the illustrated embodiments, two or more pump stages of similar dimensions can be operated in parallel by mechanically coupling the rotational parts in series as shown and by pneumatically coupling the inputs and outputs of two or more pumps in parallel to increase the flow through the parallel-connected pumps.

In alternative embodiments of the multi-stage pump, the different volumes of the cavities in each stage may be varied by changing the areas of the trochoidal cavities in certain stages and by changing the corresponding distances from the centers to the vertices of the rotors rather than changing the depths of the cavities and the thicknesses of the rotors. For example, the first rotor 300 of the first pump stage 30 may be constructed to have approximately one-half the size of the second rotor 302 of the second pump stage 32 (e.g., the nominal distance R from the center to the vertex of the first rotor may be half the nominal distance R of the second rotor) and the inner perimeter surface of the first cavity may be sized accordingly. If the depths of the first and second cavities are the same and if the first rotor is operated at the same rotational rate as the second rotor, the pumping volume of the first rotor will be correspondingly smaller since the first rotor sweeps through a smaller area. The different volumes may also be accomplished with a combination of different rotor sizes (e.g., values of R), cavity depths and rotor thicknesses.

In further alternative embodiments, other spur gears or other internal gears having differing numbers of teeth can be substituted for the spur gear, the internal gear or both described herein in order to modify the path followed by the vertices of each rotor. The shape of the cavities is modifiable to conform to the path of the rotor tips. Although the embodiments described herein include generally triangular rotor, the rotors can be constructed in other shapes with vertices that follow different trochoidal paths in accordance with the gear ratios and the equations that define the movements of the vertices caused by the interactions of the spur gear and the internal gear.

One skilled in art will appreciate that the foregoing embodiments are illustrative of the present invention. The present invention can be advantageously incorporated into alternative embodiments while remaining within the spirit and scope of the present invention, as defined by the appended claims. 

1. A pump comprising: a first stage comprising a first trochoidal-shaped cavity having a first volume, the first stage having a first input port and a first output port; a first rotor that rotates eccentrically within the first cavity about a first cam; a second stage comprising a second trochoidal-shaped cavity having a second volume greater than the first volume, the second stage having a second input port and a second output port; a second rotor that rotates eccentrically within the second cavity about a second cam; a common shaft that rotates the first cam and the second cam; and a first interconnection conduit that couples the second output port to the first input port.
 2. The pump as defined in claim 1, wherein the first cavity has substantially the same shape and area as the second cavity and wherein the second cavity has a greater depth than the first cavity.
 3. The pump as defined in claim 1, wherein the first rotor and the second rotor have substantially the same area and wherein the second rotor has a greater thickness than the first rotor.
 4. The pump as defined in claim 1, wherein each vertex of each of the first rotor and the second rotor has a continuous, uninterrupted contour.
 5. The pump as defined in claim 1, wherein each of the first output port and the second output port has a respective check valve that opens to allow gas to exit the respective cavity via the respective output port when the pressure on the side of the check valve proximate the cavity is sufficiently greater than the pressure on the opposite side of the check valve and that closes to prevent gas from entering the respective cavity via the respective output port when the pressure on the side of the check valve proximate the cavity is insufficient to force the check valve open.
 6. The pump as defined in claim 5, where the second input port has a check valve that opens to allow gas to enter the second cavity and that closes to prevent gas from exiting the second cavity via the second input port.
 7. The pump as defined in claim 6, wherein the input check valve and the output check valves comprise umbrella valves.
 8. The pump as defined in claim 1, wherein the second input port is pneumatically coupled to a system to evacuate gas from the system to reduce the pressure in the system.
 9. The pump as defined in claim 8, wherein the first output port discharges the gas at a higher pressure than the pressure in the system.
 10. The pump as defined in claim 1, wherein: the first rotor is positioned between a first cover and a second cover within the first cavity and rotates in a plane parallel to the first cover and the second cover; the first rotor has a first face proximate to and spaced apart from the first cover and has a second face proximate to and spaced apart from the second cover; and each of the first face and the second face of the rotor has a plurality of slots formed therein perpendicular to the face, the plurality of slots on each face functioning as a respective labyrinth seal to reduce the flow of gas across each face between each face and the respective cover.
 11. The pump as defined in claim 1, further comprising: a third stage comprising a third trochoidal-shaped cavity having a third volume greater than the second volume, the third stage having a third input port and a third output port; a third rotor that rotates eccentrically within the third cavity about a third cam, the third cam rotated by the common shaft; and a second interconnection conduit that couples the third output port to the second input port.
 12. The pump as defined in claim 1, further comprising: a third stage comprising a third trochoidal-shaped cavity having a third volume greater than the second volume, the third stage having a third input port and a third output port; a third rotor that rotates eccentrically within the third cavity about a third cam, the third cam rotated by the common shaft; a second interconnection conduit that couples the third output port to the second input port; a fourth stage comprising a fourth trochoidal-shaped cavity having a fourth volume greater than the third volume, the fourth stage having a fourth input port and a fourth output port; a fourth rotor that rotates eccentrically within the fourth cavity about a fourth cam, the fourth cam rotated by the common shaft; a third interconnection conduit that couples the fourth output port to the third input port.
 13. The pump as defined in claim 12, wherein: the fourth input port is coupled to a system from which gas is to be evacuated, and the fourth pump stage draws gas from the system into the fourth cavity to reduce the pressure in the system to a system pressure and outputs the gas to the third stage via the third interconnection conduit at a fourth stage output pressure that is higher than the system pressure; the third pump stage increases the pressure of the gas from the fourth stage output pressure to a third stage output pressure and outputs the gas to the second stage via the second interconnection conduit; the second pump stage increases the pressure of the gas from the third stage output pressure to a second stage output pressure and outputs the gas to the first stage via the first interconnection conduit; and the first pump stage increases the pressure of the gas from the second stage output pressure to atmospheric pressure and outputs the gas via the first output port.
 14. The pump as defined in claim 1, wherein: the first trochoidal-shaped cavity includes a first cavity lobe and a second cavity lobe, the first cavity lobe coupled to the first input port, the second cavity lobe coupled to the first output port; and an internal interconnection passage having an inlet positioned in the first cavity lobe and having an outlet positioned in the second cavity lobe, the internal interconnection passage transferring gas from the first cavity lobe to the second cavity lobe when a vertex of the first rotor is positioned between the inlet and the outlet.
 15. A pump comprising: a first stage comprising: a first enclosure having a first inner cavity having a first volume, the first inner cavity defined by a first inner surface with a trochoidal shape; a first circular cam having a first central axis and having a first eccentric axis offset from the first central axis, the first circular cam mounted in the first cavity to rotate about the first eccentric axis; a first rotor mounted to rotate about the first central axis of the first circular cam, the first rotor having a plurality of vertices that move along the first inner surface of the first inner cavity; a first input port to enable gas to enter the first inner cavity; a first output port to enable gas to exit from the first inner cavity; a second stage comprising: a second enclosure having a second inner cavity having a second volume, the second volume greater than the first volume, the second inner cavity defined by a second inner surface with a trochoidal shape; a second circular cam having a second central axis and having a second eccentric axis offset from the second central axis, the second circular cam mounted in the second cavity to rotate about the second eccentric axis; a second rotor mounted to rotate about the second central axis of the second circular cam, the second rotor having a plurality of vertices that move along the second inner surface of the second inner cavity; a second input port to enable gas to enter the second inner cavity; a second output port to enable gas to exit from the second inner cavity; a common shaft that rotates the first circular cam around the first eccentric axis and that rotates the second circular cam around the second eccentric axis at an input rate, the first rotor rotating about the first circular cam at first rotation rate that is a first fixed fraction of the input rate, the second rotor rotating about the second circular cam at a second rotation rate that is a second fixed fraction of the input rate; and an interconnection conduit that couples the second output port to the first input port.
 16. The pump as defined in claim 15, wherein the first rotation rate and the second rotation rate are the same.
 17. A four-stage vacuum pump comprising: a first stage comprising a first trochoidal-shaped cavity having a first volume and having a first rotor that rotates within the first cavity, the first stage receiving a gas at an input pressure and outputting the gas at a second pressure higher than the input pressure; a second stage comprising a second trochoidal-shaped cavity having a second volume and having a second rotor that rotates within the second cavity, the second stage receiving the gas from the first stage at the second pressure and outputting the gas at a third pressure higher than the second pressure; a third stage comprising a third trochoidal-shaped cavity having a third volume and having a third rotor that rotates within the third cavity, the third stage receiving the gas from the second stage at the third pressure and outputting the gas at a fourth pressure higher than the third pressure; a fourth stage comprising a fourth trochoidal-shaped cavity having a fourth volume and having a fourth rotor that rotates within the fourth cavity, the fourth stage receiving the gas from the third stage at the fourth pressure and outputting the gas at an exhaust higher than the fourth pressure; and a common shaft that rotates a first eccentric cam, a second eccentric cam, a third eccentric cam and a fourth eccentric cam, the first rotor rotates about the first eccentric cam, the second rotor rotates about the second eccentric cam, the third rotor rotates about the third eccentric cam, and the fourth rotor rotates about the fourth eccentric cam.
 18. The pump as defined in claim 17, wherein the first volume is greater than the second volume, the second volume is greater than the third volume, and the third volume is greater than the fourth volume.
 19. The pump as defined in claim 17, wherein each stage has at least one intake phase and at least one exhaust phase, and wherein the cams and rotors in the stages are positioned at selected respective angular positions on the common shaft such that the rotor in a stage receiving gas from another stage is in an intake phase when the stage providing the gas is in an exhaust phase.
 20. A method of lowering the pressure at an interface, comprising: applying a rotational force to a common rotating shaft that is coupled to a first pump stage and at least a second pump stage, each pump stage having a respective trochoidal-shaped chamber and having a respective rotor positioned in the chamber to rotate about a respective eccentric cam driven by the rotating shaft, the chamber in the first pump stage having a first volume, the chamber in the second pump stage having a second volume greater than the first volume; drawing gas into the second pump stage at an intake pressure, and expelling gas from the second pump stage into the first pump stage at a second stage output pressure greater than the intake pressure; and expelling gas from the first pump stage at a first stage output pressure greater than the second stage output pressure. 